1. Field of the Invention
One embodiment of the present invention relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a charge pump circuit and a semiconductor device including the charge pump circuit.
Note that in this specification, a semiconductor device means a device that utilizes semiconductor characteristics and refers to a circuit having a semiconductor element (e.g., a transistor or a diode) and a device having such a circuit. The semiconductor device also means any device that can function by utilizing semiconductor characteristics. For example, an integrated circuit, and a chip including an integrated circuit are all semiconductor devices. Moreover, a display device, a light-emitting device, a lighting device, an electronic device, and the like include a semiconductor device in some cases.
2. Description of the Related Art
As a voltage generation circuit, a charge pump circuit including capacitors and diode-connected transistors is known (e.g., Patent Document 1). A charge pump circuit is a circuit that can generate a voltage higher or lower than an input voltage without using a coil. Therefore, a charge pump circuit can be easily integrated on one IC chip together with a processor, a memory, and the like.
A transistor in which a channel is formed in an oxide semiconductor (OS) layer such as an In—Ga—Zn oxide (In—Ga—Zn—O) layer (such a transistor is referred to as an OS transistor below) is known. The OS transistor is known to have an extremely low off-state current because an oxide semiconductor has a wider band gap than silicon. A variety of semiconductor devices that utilize OS-transistor's low off-state current characteristics have been proposed. For example, Patent Document 2 discloses a charge pump circuit. In addition, Non-Patent Document 1 discloses a nonvolatile memory. Moreover, Non-Patent Document 2 discloses a central processing unit (CPU).